wip, per-unit dssp

src/mol-model-formats/structure/mmcif/parser.ts

src/mol-model-formats/structure/mmcif/secondary-structure.ts

src/mol-model-props/computed/secondary-structure.ts

src/mol-model-props/computed/secondary-structure/dssp.ts

...rops/computed/secondary-structure/dssp/backbone-hbonds.ts

...ol-model-props/computed/secondary-structure/dssp/bends.ts

...-model-props/computed/secondary-structure/dssp/bridges.ts

...l-model-props/computed/secondary-structure/dssp/common.ts

...rops/computed/secondary-structure/dssp/dihedral-angles.ts

...-model-props/computed/secondary-structure/dssp/helices.ts

...l-props/computed/secondary-structure/dssp/protein-info.ts

...l-props/computed/secondary-structure/dssp/trace-lookup.ts

...ol-model-props/computed/secondary-structure/dssp/turns.ts

...ol-model/structure/model/properties/seconday-structure.ts

src/mol-repr/structure/visual/polymer-trace-mesh.ts

src/mol-repr/structure/visual/util/polymer/trace-iterator.ts

src/mol-theme/color/secondary-structure.ts

src/tests/browser/render-structure.ts